Many types of batteries and other power cells are known, based upon a relatively wide range of electrical couples. Among the most popular electrical couples are those containing zinc. Zinc is regarded as the highest energy couple component that can be cycled in an aqueous room temperature battery and is therefore commonly used in numerous battery and power cell applications. Depending on the type of coupling partner such zinc containing batteries will exhibit various characteristic properties.
For example, zinc is coupled with carbon in most simple flashlight batteries to provide a relatively inexpensive and reliable power source. Although manufacture of Zn/C batteries is generally simple and poses only relatively little environmental impact, various disadvantages of Zn/C batteries exist. Among other things, the ratio of power to weight in commonly used Zn/C batteries is relatively poor. To improve the ratio of power to weight, alternative coupling partners and systems can be employed. For example, zinc can be coupled with mercury oxide or silver to achieve an improved power to weight ratio. However, the toxicity of mercury oxide is frequently problematic in manufacture and tends to become even more problematic when such batteries are discarded. On the other hand, while silver as a coupling partner for zinc is environmentally substantially neutral and significantly improves the power to weight ratio, the use of silver is in many instances economically prohibitive.
In still further known batteries and power cells, zinc is coupled with still other metals such as nickel or copper to provide a specific desired characteristic. However, and depending on the particular metal, new disadvantages may arise and particularly include environmental problems with manufacture and/or disposal, relatively low power to weight ratio, and undesirably low open circuit voltage.
Moreover, halogens may be employed as a coupling partner for zinc, and most common zinc-halogen couples include zinc-bromine and zinc-chloride (e.g., for load leveling batteries). However, such battery configurations are often difficult to integrate into portable or miniaturized devices Moreover, such battery configurations typically require pumping systems and are often prone to leakage leading to significant problems due to the highly corrosive nature of the halogen-containing electrolyte.
Alternatively, oxygen may be employed as a gaseous coupling partner for zinc, thereby generally avoiding problems associated with toxicity, excessive cost for coupling partners, or spillage. Among the various advantages in this configuration, using air (i.e., oxygen) as coupling partner for zinc typically results in a relatively high power to weight ratio. Moreover, the zinc-oxygen system typically provides a relatively flat discharge curve. However, reasonable shelf life of such batteries can often only be achieved by using an airtight seal. Furthermore, to provide continuous operation, air must have an unobstructed path through the battery to the cathode so that the-oxygen in the air is available to discharge the cathode. Moreover, commercial applications of zinc-air batteries have previously been limited to primary or non-rechargeable types.
An additional problem with zinc-air batteries often arises from the use of an alkaline electrolyte, which is typically disposed between a porous zinc anode and an air cathode formed of a carbon membrane. Unfortunately, the use of alkaline electrolytes in such electrodes frequently leads to absorption of carbon dioxide, and consequently formation of carbonates, which in turn tend to reduce conductivity and clog the pores in the active surfaces of the electrodes.
Thus, although there are numerous coupling partners for zinc in batteries and power cells known in the art, all or almost all of them suffer from one or more disadvantage. Therefore, there is still a need to provide compositions and methods for improved batteries.